Use of a cylindrical test body

ABSTRACT

The invention relates to the use of a cylindrical test body with one or more spherical cavities for testing the function and defect recognition quality of systems for the automatic recognition of defects in castings and method for the manufacture thereof. All the prior art testing possibilities are not in accordance with practice and suffer from different advantages. The invention surprisingly obviates this problem by the use of a cylindrical test body with one or more spherical cavities for testing the function and defect recognition quality of systems for the automatic recognition of defects in castings and which is fixed on or in the casting to be tested. Thus, the invention has created test bodies or objects, which better approximate the shape of natural defects and which are simple and inexpensive to manufacture in reproducible manner. These test bodies contain one or more spherical cavities optionally having different sizes and positions.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to the use of a cylindrical test body with one or more spherical cavities for testing the function and defect recognition quality of systems for the visual or automatic recognition of defects in castings and a method for the manufacture thereof.

[0003] 2. Description of the Related Art

[0004] Modern systems for the automatic recognition of defects in castings, so-called ADR systems (automatic defect recognition) must be able to reliably detect ever smaller defects. The smallest attenuations and interferences in the signal chain can lead to defects no longer being reliably detected. At the same time the presently used methods for enabling conclusions to be drawn concerning defects and defect sizes by means of 2D/3D filming, require an adaptation in accordance with practice, so that in the forefront of the interpretation of an ADR system a valid statement can be made concerning the possible recognition quality.

[0005] In conventionally used methods, the function of the system is tested with wire penetrameters, e.g. DIN 54109 or platinum double wire webs (standard EN 13068-3), or by means of inspection parts provided with clearly defined bores; or perforated plates applied to inspection parts, e.g. ASTM E-1025.

[0006] All these testing and inspection possibilities are not really in accordance with practice. The first unit only tests the resolution and cannot be used for detection purposes. The second unit is scarcely reproducible, because the drilling depths are individually set, the drilled hole is conical and as a result of the cylindrical shape of the hole or bore, the transmission direction has a considerable influence on recognition. The third possibility, using a penetrameter, suffers from the same problem that the detectable size of the objects is dependent to a significant extent on the transmission direction as a result of the cylindrical geometry. In addition, the sharp edges of the bores provide contrasts not in accordance with 3D defect practice. The first and third methods also suffer from the fact that the test bodies cannot be fixed to the part to be inspected in the installation and then allow an automatic installation calibration. Therefore the problem of the invention is to improve the testing and inspection possibilities for the operation and defect recognition quality of ADR systems, whilst providing an economic method for the manufacture of the test bodies used for this purpose.

[0007] Surprisingly this problem is solved by the use of a cylindrical test body with a spherical cavity for testing the function and defect recognition quality of systems for the automatic recognition of defects in castings and fixed on or in the casting to be tested.

[0008] The invention creates test objects or bodies, which better approximate the shape of natural defects and which can be manufactured easily and inexpensively in a reproducible manner. These test bodies contain one or more spherical cavities optionally of different sizes and positions. Thus, the invention makes it possible to obviate the use of wire penetrameters, defined conical bores and perforated plates.

[0009] The method of the invention for the manufacture of said cylindrical test body offers the three following alternatives:

[0010] 1)

[0011] a. Punching circular holes, whose diameter approximates in optimum manner the shape of a ball, in the center of a plurality of foil layers, which are made from the material of a casting to be tested.

[0012] b. Superimposing the plurality of foil layers with the punched holes and adjacent to the foil layers with the smallest holes are superimposed foil layers without a hole.

[0013] c. Pressing or bonding together the superimposed plurality of foil layers.

[0014] or

[0015] 2)

[0016] a. Provision of two cylindrical test body pieces with the same diameter.

[0017] b. Drilling a hemispherical recess in one end face of each cylindrical test body piece.

[0018] c. Assembly by means of bonding of the test body pieces at the end faces thereof.

[0019] or

[0020] 3)

[0021] a. Provision of a circular recess in one test body piece and a corresponding circular insert in facing manner on the other test body piece and drilling a semicircular recess in facing sides of the test body piece or circular insert, and

[0022] c. Pressing the circular insert into the circular recess.

SUMMARY OF THE INVENTION

[0023] The invention provides a cylindrical test body comprising one or more spherical cavities for testing the function and defect recognition quality of systems for the automatic recognition of defects in castings fixed on or in the casting to be tested.

[0024] The invention also provides a method for the manufacture of a cylindrical test body with one or more spherical cavities comprising I, II or III:

[0025] I.

[0026] a) punching circular holes, whose diameter approximates in optimum manner the shape of a ball, in the center of a plurality of foil layers, which are made from the material of a casting to be tested,

[0027] b) superimposing of the plurality of foil layers with the punched holes and adjacent to the foil layers with the smallest holes are superimposed foil layers without a hole,

[0028] c) pressing or bonding together the superimposed plurality of foil layers;

[0029] II.

[0030] a) provision of two cylindrical test body pieces with the same diameter,

[0031] b) drilling a hemispherical recess in one end face of each cylindrical test body piece,

[0032] c) assembly by means of bonding of the test body pieces at the end faces thereof;

[0033] III.

[0034] a) provision of a circular recess in one test body piece and a corresponding circular insert in facing manner on the other test body piece and drilling a semicircular recess in facing sides of the test body piece or circular insert, and

[0035] b) pressing the circular insert into the circular recess.

[0036] The invention further provides cylindrical test body for testing the function and quality of a defect recognition system, which cylindrical test body is formed by the steps of I, II, or III:

[0037] I.

[0038] a) providing a plurality of circular foil layers, which foil layers comprise a material of a casting to be tested;

[0039] b) forming a circular hole in some of the foil layers, whereby the circular holes are sufficiently sized and aligned such that, upon superimposing the plurality of foil layers, the circular holes are capable of defining a central spherical cavity within the superimposed plurality of foil layers;

[0040] c) superimposing the plurality of foil layers such that the circular holes define a central spherical cavity within the superimposed plurality of foil layers, and such that those foil layers with the smallest holes are superimposed against foil layers without holes, and

[0041] d) attaching the superimposed plurality of foil layers to form a cylindrical test body having a central spherical cavity;

[0042] II.

[0043] a) providing first and second cylindrical test body pieces of substantially the same diameter, wherein each test body piece has an end face which faces the other test body piece;

[0044] b) forming a hemispherical recess within in one end face of each cylindrical test body piece, and

[0045] c) attaching the end face of the first test body piece to the end face of the second test body piece to thereby form a cylindrical test body, and wherein the hemispherical recesses are sufficiently aligned to thereby define a central spherical cavity within the cylindrical test body;

[0046] III.

[0047] a) providing first and second test body pieces having a height H, thickness T, and diameter Dm, and each test body piece further comprising a hemispherical recess having a diameter Dz;

[0048] b) providing a spherical insert having substantially the same diameter as the hemispherical recesses;

[0049] c) placing the spherical insert within the hemispherical recess of the first test body piece such that a first half of the spherical insert is within the hemispherical recess and a second half of the spherical insert faces the second test body piece; and

[0050] d) placing the second test body piece onto the second half of the spherical insert to thereby attach the first and second test body pieces, thus forming a cylindrical test body with a central spherical insert.

[0051] The invention still further provides a process for testing the function and quality of a defect recognition system, which process comprises the steps of: i) providing a cylindrical test body for testing the function and quality of a defect recognition system, which cylindrical test body is formed by the steps of I, II, or III:

[0052] I.

[0053] a) providing a plurality of circular foil layers, which foil layers comprise a material of a casting to be tested;

[0054] b) forming a circular hole in some of the foil layers, whereby the circular holes are sufficiently sized and aligned such that, upon superimposing the plurality of foil layers, the circular holes are capable of defining a central spherical cavity within the superimposed plurality of foil layers;

[0055] c) superimposing the plurality of foil layers such that the circular holes define a central spherical cavity within the superimposed plurality of foil layers, and such that those foil layers with the smallest holes are superimposed against foil layers without holes, and

[0056] d) attaching the superimposed plurality of foil layers to form a cylindrical test body having a central spherical cavity;

[0057] II.

[0058] a) providing first and second cylindrical test body pieces of substantially the same diameter, wherein each test body piece has an end face which faces the other test body piece;

[0059] b) forming a hemispherical recess within in one end face of each cylindrical test body piece, and

[0060] c) attaching the end face of the first test body piece to the end face of the second test body piece to thereby form a cylindrical test body, and wherein the hemispherical recesses are sufficiently aligned to thereby define a central spherical cavity within the cylindrical test body;

[0061] III.

[0062] a) providing first and second test body pieces, each having a height H, thickness T, and diameter Dm, and each test body piece further comprising a hemispherical recess having a diameter Dz, such that the first and second test body pieces are capable of forming a central spherical cavity upon attaching the test body pieces together;

[0063] b) providing a spherical insert having substantially the same diameter as the hemispherical recesses;

[0064] c) placing the spherical insert within the hemispherical recess of the first test body piece such that a first half of the spherical insert is within the hemispherical recess and a second half of the spherical insert faces the second test body piece; and

[0065] d) placing the second test body piece onto the second half of the spherical insert to thereby attach the first and second test body pieces, thus forming a cylindrical test body having a central spherical cavity which contains the spherical insert;

[0066] ii) providing an automatic defect recognition system comprising a defect detector;

[0067] iii) measuring the spherical cavity of the cylindrical test body in three dimensions with the defect detector, to test the image quality of the defect detector and to calibrate the defect detector.

BRIEF DESCRIPTION OF THE DRAWINGS

[0068]FIG. 1a shows a perspective view of a test body used according to the invention in the structure based on the foil principle.

[0069]FIG. 1b shows a cross-sectional view of the test body of FIG. 1a.

[0070]FIG. 2a shows a diagrammatic perspective view of a further, not yet assembled test body based on the half-body principle.

[0071]FIG. 2b shows a diagrammatic cross-sectional view through the test body of FIG. 2a.

[0072]FIG. 3 shows a diagrammatic cross-sectional view through another embodiment of a test body according to the invention prior to its assembly.

[0073]FIG. 4a shows a perspective view of another embodiment of a test body according to the invention with several spherical cavities prior to assembly.

[0074]FIG. 4b shows a horizontal section through the test body of FIG. 4a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0075] In FIG. 1a the cylindrical test body produced according to the first manufacturing variant carries the reference numeral 10. It has 20 foil layers, which are congruently superimposed and in all give a thickness=T of the test body 10, the layer thickness of the individual foils being e.g. 20 or 50 μm. It is clear that other values are readily conceivable.

[0076] In FIG. 1b the hole punched centrally in each coil carries the reference numeral 12. The diameter for the foil or hole (Dm, dn) is given in Table 1 or 2.

[0077] It is possible to build up from a set of 100 foils having in each case a thickness of e.g. 20 μm and punched out holes with diameters, as shown in Table 2, from 0.2 mm to the maximum diameter, all desired cavity sizes for a test body with a thickness of 2 mm. The superimposed foil layers can be pressed together at each comer by two plastic or aluminum plates using in each case one screw or are bonded with an adhesive, which is scarcely X-ray absorbing. The foil layer material corresponds to that to be tested, e.g. aluminum. It is clear that the test bodies are fixed on or in the casting to be tested at an appropriate point.

[0078] In the second method variant, in two cylindrical test body pieces are made in each case two hemispherical holes or recesses 13, 14, so that a spherical cavity is obtained on assembly, as shown in FIG. 2a. The body pieces are then bonded together.

[0079] According to another embodiment, for adhesive-free assembly, a somewhat larger circular insert 16 can be inserted in the test body piece and is then pressed together with the other test body piece having a circular recess 15. The basic structure is shown in FIG. 3.

[0080] In order to be able to simulate defect groups, it is also possible to make several holes with the same or different diameters (cf. FIG. 4a+b). When using different diameters it is possible to determine with a single test body the defect recognizability limit quantity.

[0081] Fundamentally the test body according to the invention is cylindrical or rod-shaped, so that by means of a bore identical to the external diameter the test body can be introduced positively into a casting to be tested. The thus prepared casting to be tested can be used as a measurement part for an X-ray system. On passing through the system information is provided as to whether defects of this size can be reliably detected by the system.

[0082] The use of a test body according to the invention offers the following advantages:

[0083] The detectable defect size is independent of the transmission direction (because there are spherical 3D cavities). There is a defect approximation in 3D instead of 2D—test bodies for 3D calibration with potential for 3D defect depth measurement of defects. The test body tests both the image quality of the detector and the detection by the software. Optionally groups of identical cavities can be made in order to e.g. simulate shrink holes and only in this way can group defect recognition be measured. It is also possible to make groups of different cavities in order in this way to determine the recognizability limit with a single test object (similar to line pattern with 2D). With considerable variations, test bodies are easy, inexpensive and reproducible to manufacture. TABLE 1 Example for Test Body Diameter (D_(m)) for Various Thicknesses T by the Foil Method Diameter of the Thickness T in MM Test Body in mm 1 2 5 10 Diameter (D1) 5 X X Diameter (D2) 10 X X X Diameter (D3) 20 X X X Diameter (D5) 40 X X Diameter (D5) 60 X

[0084] TABLE 2 Hole Diameter d_(n) of the individual Films With T = 2 mm Thickness of the test Body 2 mm Thickness 0,2 Hole diameter Units in μm, if not otherwise described Layer/μm 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 20 0 0 0 0 0 0 0 0 0 0 0 20 0 0 0 0 0 0 0 0 0 282 40 0 0 0 0 0 0 0 0 0 486 60 0 0 0 0 0 0 0 0 0 624 80 0 0 0 0 0 0 0 0 0 735 100 0 0 0 0 0 0 0 0 0 829 120 0 0 0 0 0 0 0 0 268 912 140 0 0 0 0 0 0 0 0 461 986 160 0 0 0 0 0 0 0 0 592 1054 180 0 0 0 0 0 0 0 0 696 1116 200 0 0 0 0 0 0 0 0 785 1173 220 0 0 0 0 0 0 0 252 862 1226 240 0 0 0 0 0 0 0 434 932 1276 260 0 0 0 0 0 0 0 557 995 1323 280 0 0 0 0 0 0 0 655 1053 1367 300 0 0 0 0 0 0 0 737 1106 1408 320 0 0 0 0 0 0 236 810 1156 1448 340 0 0 0 0 0 0 405 874 1202 1485 360 0 0 0 0 0 0 520 933 1245 1520 380 0 0 0 0 0 0 610 986 1285 1553 400 0 0 0 0 0 0 687 1035 1323 1585 420 0 0 0 0 0 218 753 1081 1359 1615 440 0 0 0 0 0 375 813 1123 1393 1643 460 0 0 0 0 0 480 866 1162 1425 1670 480 0 0 0 0 0 562 915 1198 1455 1696 500 0 0 0 0 0 632 959 1233 1483 1720 520 0 0 0 0 199 693 1000 1265 1510 1743 540 0 0 0 0 341 746 1037 1295 1535 1765 560 0 0 0 0 436 794 1072 1323 1559 1786 580 0 0 0 0 510 837 1105 1349 1581 1806 600 0 0 0 0 572 876 1135 1374 1602 1824 620 0 0 0 178 626 912 1163 1397 1622 1842 640 0 0 0 304 673 945 1188 1419 1641 1858 660 0 0 0 387 714 975 1212 1439 1658 1873 680 0 0 0 452 751 1002 1235 1458 1675 1888 700 0 0 0 506 785 1027 1255 1475 1690 1901 720 0 0 154 551 815 1051 1274 1491 1704 1914 740 0 0 262 590 842 1072 1292 1506 1717 1926 760 0 0 332 624 866 1091 1308 1520 1729 1936 780 0 0 385 655 888 1108 1322 1532 1740 1946 800 0 0 428 681 908 1124 1336 1544 1750 1955 820 0 125 464 704 925 1138 1347 1554 1759 1964 840 0 211 494 724 940 1151 1358 1563 1768 1971 860 0 265 520 742 954 1162 1367 1572 1775 1977 880 0 304 541 757 966 1171 1376 1579 1781 1983 900 0 334 558 769 975 1180 1383 1585 1787 1988 920 87 357 572 779 984 1186 1388 1590 1791 1992 940 143 375 583 788 990 1192 1393 1594 1795 1995 960 173 387 592 794 995 1196 1396 1597 1797 1997 980 191 395 597 798 998 1198 1399 1599 1799 1999 1000 199 399 600 800 1000 1200 1400 1600 1800 2000

[0085] Thickness T in mm Diameter D_(m) of the Test body in mm 1 2 5 10 Diameter (D1) 15 X X X Diameter (D-5) 12 X X X

[0086] TABLE 3 Hole Diameter d_(n) for the various Embodiment of the Test Body Thickness of Bored Hemispherical measure d_(n) in mm; the Test Body 0.2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,1 1,3 1,4 1,5 1,6 1,8 2 Diameter D1 5 1 # # # # # # # Diameter D1 5 2 # # # # # # # # # # # # # # # # Diameter D1 5 5 # # # # # # # # # # # # # # # # # Diameter D2 12 2 # # # # # # # # # # # # # Diameter D2 12 5 # # # # # # # # # Diameter D2 12 10 # Diameter D1 5 1 Diameter D1 5 2 Diameter D1 5 5 # # # # # # # # Diameter D2 12 2 Diameter D2 12 5 # # # # # # # # Diameter D2 12 10 # # # # # # # # # # # # # # # # #

[0087] While the present invention has been particularly shown and described with reference to preferred embodiments, it will be readily appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the claims be interpreted to cover the disclosed embodiment, those alternatives which have been discussed above and all equivalents thereto. 

What is claimed is:
 1. A cylindrical test body comprising one or more spherical cavities for testing the function and defect recognition quality of systems for the automatic recognition of defects in castings fixed on or in the casting to be tested.
 2. A method for the manufacture of a cylindrical test body with one or more spherical cavities comprising I, II or III: I. a) punching circular holes, whose diameter approximates in optimum manner the shape of a ball, in the center of a plurality of foil layers, which are made from the material of a casting to be tested, b) superimposing of the plurality of foil layers with the punched holes and adjacent to the foil layers with the smallest holes are superimposed foil layers without a hole, c) pressing or bonding together the superimposed plurality of foil layers; II. a) provision of two cylindrical test body pieces with the same diameter, b) drilling a hemispherical recess in one end face of each cylindrical test body piece, c) assembly by means of bonding of the test body pieces at the end faces thereof; III. a) provision of a circular recess in one test body piece and a corresponding circular insert in facing manner on the other test body piece and drilling a semicircular recess in facing sides of the test body piece or circular insert, and b) pressing the circular insert into the circular recess.
 3. The method of claim 2 comprising: I. a) punching circular holes, whose diameter approximates in optimum manner the shape of a ball, in the center of a plurality of foil layers, which are made from the material of a casting to be tested, b) superimposing of the plurality of foil layers with the punched holes and adjacent to the foil layers with the smallest holes are superimposed foil layers without a hole, c) pressing or bonding together the superimposed plurality of foil layers.
 4. The method of claim 2 comprising: II. a) provision of two cylindrical test body pieces with the same diameter, b) drilling a hemispherical recess in one end face of each cylindrical test body piece, c) assembly by means of bonding of the test body pieces at the end faces thereof.
 5. The method of claim 2 comprising: III. a) provision of a circular recess in one test body piece and a corresponding circular insert in facing manner on the other test body piece and drilling a semicircular recess in facing sides of the test body piece or circular insert, and b) pressing the circular insert into the circular recess.
 6. The method according to claim 2, wherein the bonding of the test body pieces takes place with a metal-free adhesive.
 7. The method according to claim 2, wherein the diameter (Dz) of the recess is ⅝ of the diameter (Dm) of the test body pieces, and wherein the height (H) is {fraction (2/8)} of the thickness (T).
 8. The method according to claim 7 wherein the diameter in the upper, drilled part and in the lower, milled part are dimensioned in such a way that there is a force fit between these parts.
 9. The method according to claim 7, wherein the diameter in the upper, drilled part and in the lower, milled part are dimensioned in such a way that there is a force fit between these parts.
 10. A cylindrical test body for testing the function and quality of a defect recognition system, which cylindrical test body is formed by the steps of I, II, or III: I. a) providing a plurality of circular foil layers, which foil layers comprise a material of a casting to be tested; b) forming a circular hole in some of the foil layers, whereby the circular holes are sufficiently sized and aligned such that, upon superimposing the plurality of foil layers, the circular holes are capable of defining a central spherical cavity within the superimposed plurality of foil layers; c) superimposing the plurality of foil layers such that the circular holes define a central spherical cavity within the superimposed plurality of foil layers, and such that those foil layers with the smallest holes are superimposed against foil layers without holes, and d) attaching the superimposed plurality of foil layers to form a cylindrical test body having a central spherical cavity; II. a) providing first and second cylindrical test body pieces of substantially the same diameter, wherein each test body piece has an end face which faces the other test body piece; b) forming a hemispherical recess within in one end face of each cylindrical test body piece, and c) attaching the end face of the first test body piece to the end face of the second test body piece to thereby form a cylindrical test body, and wherein the hemispherical recesses are sufficiently aligned to thereby define a central spherical cavity within the cylindrical test body; III. a) providing first and second test body pieces having a height H, thickness T, and diameter Dm, and each test body piece further comprising a hemispherical recess having a diameter Dz; b) providing a spherical insert having substantially the same diameter as the hemispherical recesses; c) placing the spherical insert within the hemispherical recess of the first test body piece such that a first half of the spherical insert is within the hemispherical recess and a second half of the spherical insert faces the second test body piece; and d) placing the second test body piece onto the second half of the spherical insert to thereby attach the first and second test body pieces, thus forming a cylindrical test body with a central spherical insert.
 11. The cylindrical test body of claim 10 wherein the foil layers or the test body pieces comprise aluminum.
 12. The cylindrical test body of claim 10, wherein the foil layers or the test body pieces are attached via a metal-free adhesive.
 13. The cylindrical test body of claim 10, wherein the diameter (Dz) of the recess is about ⅝ of the diameter (Dm) of the test body pieces, and wherein the height (H) is about {fraction (2/8)} of the thickness (T).
 14. A process for testing the function and quality of a defect recognition system, which process comprises the steps of: i) providing a cylindrical test body for testing the function and quality of a defect recognition system, which cylindrical test body is formed by the steps of I, II, or III: I. a) providing a plurality of circular foil layers, which foil layers comprise a material of a casting to be tested; b) forming a circular hole in some of the foil layers, whereby the circular holes are sufficiently sized and aligned such that, upon superimposing the plurality of foil layers, the circular holes are capable of defining a central spherical cavity within the superimposed plurality of foil layers; c) superimposing the plurality of foil layers such that the circular holes define a central spherical cavity within the superimposed plurality of foil layers, and such that those foil layers with the smallest holes are superimposed against foil layers without holes, and d) attaching the superimposed plurality of foil layers to form a cylindrical test body having a central spherical cavity; II. a) providing first and second cylindrical test body pieces of substantially the same diameter, wherein each test body piece has an end face which faces the other test body piece; b) forming a hemispherical recess within in one end face of each cylindrical test body piece, and c) attaching the end face of the first test body piece to the end face of the second test body piece to thereby form a cylindrical test body, and wherein the hemispherical recesses are sufficiently aligned to thereby define a central spherical cavity within the cylindrical test body; III. a) providing first and second test body pieces, each having a height H, thickness T, and diameter Dm, and each test body piece further comprising a hemispherical recess having a diameter Dz, such that the first and second test body pieces are capable of forming a central spherical cavity upon attaching the test body pieces together; b) providing a spherical insert having substantially the same diameter as the hemispherical recesses; c) placing the spherical insert within the hemispherical recess of the first test body piece such that a first half of the spherical insert is within the hemispherical recess and a second half of the spherical insert faces the second test body piece; and d) placing the second test body piece onto the second half of the spherical insert to thereby attach the first and second test body pieces, thus forming a cylindrical test body having a central spherical cavity which contains the spherical insert; ii) providing an automatic defect recognition system comprising a defect detector; iii) measuring the spherical cavity of the cylindrical test body in three dimensions with the defect detector, to test the image quality of the defect detector and to calibrate the defect detector.
 15. The process of claim 14 wherein groups of identical cavities are formed within the cylindrical test body to thereby measure group defect recognition of the defect detector.
 16. The process of claim 14 wherein a plurality of cavities are formed within the cylindrical test body to thereby determine the recognizability limit of the defect detector using a single cylindrical test body.
 17. The process of claim 14 wherein the foil layers or the test body pieces comprise aluminum.
 18. The process of claim 14 wherein the foil layers or the test body pieces are attached via a metal-free adhesive.
 19. The process of claim 14 wherein the diameter (Dz) of the recess is about ⅝ of the diameter (Dm) of the test body pieces, and wherein the height (H) is about {fraction (2/8)} of the thickness (T). 